The present invention relates to a method for joining fiber-reinforced plastics materials. The present invention therefore relates to a method for joining, in particular for welding, fiber-reinforced joining partners, formed from a plastics material, at the connection faces thereof by use of an ultrasonic welding method, wherein for increasing the strength of the connection a concentrator and/or an insert are/is embedded into the joint.
On account of the ongoing development of plastics materials and on account of the clean and simple handling of these materials, connecting thermoplastic base materials by means of ultrasonic welding has rapidly established itself. The “unreleasable” connection produced by means of ultrasonic welding may be applied in the most varied technical fields and with the most varied plastics materials.
In the case of ultrasonic welding using a simultaneously applied force, the induced oscillations by way of boundary surface friction and sound absorption are converted to melting heat. The joint material congeals within the welding zone of the two joining parts and post cooling forms an almost homogenous connection. The strength of the seam may be influenced in particular by way of modifying the profile of the amplitude and/or of the force.
Various devices and methods for welding using ultrasound are known in the prior art. In particular, a device for ultrasonic welding of thermoplastic materials is known from DE 1804988 B, wherein a sonotrode having an elongated apex and a mating face are pressed together and are disposed in relation to one another, wherein the device may find an application in the case of various types of materials, such as sheet material of various thickness, having even relatively large dimensions. Using such a device, in particular woven fabrics which are produced from thermoplastic fibers or at least contain thermoplastic fibers in conjunction with natural fibers, for example a blend of polyester fibers or cotton, may also be interconnected.
A further method for producing a materially-integral connection between workpieces is known from DE 10 2010 038 470. This method has the following steps: providing a workpiece having a metal surface, which on at least one fusing face has a coating containing thermoplastics; providing a workpiece having a thermoplastic surface; placing together the fusing surface and the workpiece having the thermoplastic surface; welding together the workpiece having the metal surface and the workpiece having the thermoplastic surface on the fusing face by ultrasonic action.
An ultrasonic device for welding metal foils, in particular aluminum foils, which are coated with plastics material, which device has a sonotrode excited by means of an emitter and an amplifier, such as are usually found in conventional ultrasonic welding apparatuses, and a support block on which the foils to be welded are placed, is known from DE 2944080 A.
Furthermore, a method for welding thermoplastic materials by means of ultrasound, wherein a thin thermoplastic layer has at least one hole and wherein welding is performed exclusively in the region of the hole, is known from DE 60204002051 T2.
A method for connecting in a tight manner a container from a thermoplastic plastics material by means of ultrasound is known from AT 0334616 B, wherein the materials for producing liquid-tight casings are welded in an overlap.
However, the methods known in the prior art have various disadvantages. On the one hand, the problems lie therein that an unsatisfactory welding procedure is achieved when plastics materials having dissimilar melting points are welded.
A highly significant aspect when welding plastics materials lies in the strength of the connection point. In particular, when fiber-reinforced plastics materials are used, there is a requirement for the weld or the joint, respectively, to have sufficiently high strength and stability.
However, it is known in the case of welding fiber-reinforced plastics material that upon softening and heating the plastics materials, the endless fibers located in the fiber-reinforced plastics material on the boundary surfaces do not protrude into the joint and consequently do not contribute toward the strength of the connection. Thus, despite the use of the fiber-composite materials, the strength properties at the connection point are significantly lower in comparison with the strength of the fiber-composite material.
This means that the connection point per se is present without particle reinforcement or fiber reinforcement.
It is therefore an object of the present invention to overcome such disadvantages and to provide an improved method for joining or welding, respectively, fiber-reinforced joining partners, formed from a plastics material, in which method the joint has improved strength.
This and other objects are achieved by a method for joining fiber-reinforced joining partners, formed from a plastics material, at the connection faces thereof, wherein in the region of the connection faces a concentrator and/or an insert is applied therebetween and, by an ultrasonic welding method, is fused collectively with the connection faces in such a manner that post curing a materially integral joint as a mixing region is configured from the materials of the joining partners and of the concentrator and/or the insert.
The concept of the present invention lies in embedding a separate concentrator and/or insert into the joint of the fiber-reinforced joining partners, formed from a plastics material, so as to achieve a form-fitting and/or materially integral connection point.
A first aspect of the invention lies in embedding a concentrator, for example in the form of granulate, into the joint, so as to, on account of fusing of the granulate, create a mixing region which is configured according to the intended use.
Instead of a concentrator, a second aspect of the invention lies in using an insert having a higher melting temperature than that of the joining partners, so that the insert upon fusing of the connection faces is embedded in the latter in a form-fitting manner.
Therefore, according to the invention a method for joining fiber-reinforced joining partners, formed from a plastics material, at the connection faces thereof, is provided, wherein in the region of the connection faces a concentrator is applied therebetween and by means of an ultrasonic welding method is fused collectively with the connection faces in such a manner that post curing a materially integral joint as a mixing region is configured from the materials of the joining partners and of the concentrator.
Alternatively, furthermore a method for joining fiber-reinforced joining partners, formed from a plastics material, at the connection faces thereof, is provided, wherein in the region of the connection faces an insert is applied therebetween and by means of an ultrasonic welding method the connection faces are fused in such a manner that the insert is embedded in an materially-integral manner into the connection faces and in this way a form-fitting joint is obtained. This is preferably performed in that the melting temperature of the insert is above the melting temperature of the joining partners. On account thereof, the connection faces of the joining partners are fused and the insert may be embedded thereinto in a form-fitting manner.
Thus, an additional thermoplastic material in the form of a concentrator and/or of an insert may thus be applied prior to the actual welding process between the joining partners, where said insert according to the intended use is required for increasing strength. According to the invention, the position, the amount, and the material properties of the concentrator or of the insert here are adaptable to the process, depending on the joining task.
Potential concentrator matrix materials are to have a similar melting range and thus a similar melting temperature as the joining partners, so that a sufficiently stable connection may be produced. Preferably, two plastics materials of identical type are welded together; however, a fiber-reinforced plastics component from PA6 may also be joined using a concentrator from PA6.6 or PA12, for example.
According to the invention, an ultrasonic converter and a sonotrode are disposed in such a manner so that the two joining partners by way of mechanical oscillations are fused at the connection faces thereof and a welded connection is produced.
It is furthermore preferable for the joining partners to be composed of a thermoplastic plastics material into which a plurality of endless fibers are embedded. In this way, thermoplastic plastics materials which are reinforced with endless fibers may be selectively connected to suitable concentrators such that joints with high strength are obtained.
It is therefore particularly preferable for the concentrator used to have a fiber-reinforced or particle-reinforced plastics material. It may be ensured in this way that, upon fusing of the concentrator, fiber-reinforcement may also be achieved in the boundary surfaces and thus in the joint. Carbon fibers, carbon-based fibers, or glass fibers or carbon particles, carbon-based particles, or glass-fiber particles, or the like, may be used as a reinforcement fiber or as reinforcement particles.
In one further preferred embodiment of the invention it is provided that one or a plurality of inserts of a correspondingly adapted shape, size, and/or a selected material composition is/are embedded into the joint. In this way, even complex joining processes may be produced by a suitable selection of inserts. By way of using dissimilar materials, there is furthermore the potential for placing inserts beside one another and for the technical advantages which are offered in each case by the material of the insert to be utilized in one joint.
In one particularly preferred embodiment of the invention, it is established by way of the suitable use of concentrators and/or inserts that the joint post curing comprises in each case one upper and lower boundary surface having an interdisposed transition region, wherein a multiplicity of reinforcement fibers or elements of the insert protrude from the transition region through in each case at least one of the boundary surfaces into the respective adjacent material regions of the joining partners and thus contribute toward the strength of the connection. By way of such an ultrasonic welding connection which is produced by way of a fiber-reinforced concentrator or insert, a joint which has significantly higher strength in comparison to a joint of comparable size produced according to the prior art is obtained.
In one preferred embodiment of the invention, the concentrator is provided as granulate material. In such a case, fusing the granulate between the joining partners is performed collectively with fusing the joint faces.
Various materials are suitable as inserts. For example, a CFRTP may be employed, for example, as embedding material, or alternatively a metallic insert such as a fine-blanked component. A carbon fiber-reinforced thermoplastic insert which is embedded directly between the contact faces of the joining partners and which by the mechanical oscillations is fused together with the joining partners and post curing becomes part of the weld connection may be used as a CFRTP, for example.
A further aspect of the present invention may be seen in that such plastics materials may be used in each case as a concentrator material or as an insert material that the particular technical properties of these materials are employed.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.